The invention concerns an apparatus for granulating according to the preamble of claim 1.
Granulating apparatuses for granulating hot cut, wherein the knocked off granulates are picked up, cooled and discharged by a quickly flowing fluid film or fluid ring, for example water, are known in different embodiment forms. In the case of these apparatuses a critical area is the sealing of the knife driving shaft against the water rotating in the granulating housing. An escape of the water from the area between the shaft and the granulating housing should be prevented since the water otherwise could undesirably reach the area of the motor. For this purpose different sealings are known from prior art that seal the shaft that is rotating about its axis reasonably well.
Still more difficult the situation becomes when the shaft rotates not only about its own axis but additionally is also to be axially displaceable in order to adjust the spacing of the knifes to the perforated plate and to adjust the cutting pressure of the knifes optimally. Such granulating apparatuses, whereby the shaft that supports the knife is adjustable in the axial direction, are likewise known in a plurality of implementations. In these cases the sealing must not only prevent a water escape and endure the rotation of the shaft in the bearing, but also assure in a lasting manner the axial adjustability.
Frequently according to prior art the shaft of the knife head is thereby supported in an axially displaceable sleeve. By these means the desired contact pressure of the knifes against the perforated plate can also be adjusted. The torque is transmitted to the knife driving shaft usually by means of a toothed clutch. If water is utilized as a cooling medium for the knocked off granulate particles, which is usually the case, the knife driving shaft has to be sealed relative to the housing in order to prevent an escape of water through the bearing Hereby friction-dependent difficulties arise. The axial displacement of the knife driving shaft also causes a displacement of the running surface of a sealing ring that implements the sealing of the water, so that the friction conditions change continuously. In a similar way the friction parameters of the toothed clutch change also during the displacement of the knife driving shaft. Furthermore one should take note that the sleeve that forms the support runs in a slide bearing that has to be greased. Here also different friction parameters arise at different times because the greasing means (usually oil) becomes after some time more or less gummy so that a relatively high breakaway torque is produced which is in contrast to the demand that usually only minor axial friction is desired. Beyond that a sleeve bearing is contingent on a certain effort. A dragging support of the shaft in the housing by means of two sealing rings with an oil film positioned in between also has the disadvantage that the lifetime of a seal ends at some point and the sealings become porous and leaking, the oil film escapes and subsequently becomes affixed to the shaft and an axial displacement capability is no longer assured.
For the solution of this problem diverse implementations are known from prior art, for example the substitution of a sleeve support of the shaft by means of a motor bearing. Furthermore different suspensions of the motors were developed, for example in the DE 10 302 645 or the WO 2006/122340, in order to assure the axial displacement capability of the knife driving shaft for the long term.